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Design of external microtextures for efficient light outcoupling in OLEDs with different preferential orientation of emission dipoles

Kovačič Milan

Opto-Electronics Review

2022

Vol. 30, No. 2

art. no. e141542

External light outcoupling structures provide a cost-effective and highly efficient solution for light extraction in organic light-emitting diodes. Among them, different microtextures, mainly optimized for devices with isotopically oriented emission dipoles, have been proposed as an efficient light extraction solution. In the paper, the outcoupling for a preferential orientation of emission dipoles is studied for the case of a red bottom-emitting organic light-emitting diode. Optical simulations are used to analyse the preferential orientation of dipoles in combination with three different textures, namely hexagonal array of sine-textures, three-sided pyramids, and random pyramids. It is shown that while there are minimal differences between the optimized textures, the highest external quantum efficiency of 51% is predicted by using the three-sided pyramid texture. Further improvements, by employing highly oriented dipole sources, are examined. In this case, the results show that the top outcoupling efficiencies can be achieved with the same texture shape and size, regardless of the preferred orientation of the emission dipoles. Using an optimized three-sided pyramid in combination with ideally parallel oriented dipoles, an efficiency of 62% is achievable. A detailed analysis of the optical situation inside the glass substrate, dominating external light outcoupling, is presented. Depicted results and their analysis offer a simplified further research and development of external light extraction for organic light-emitting devices with highly oriented dipole emission sources.

Modeling of light extraction efficiency of scattering thin film using Mie scattering

Cheong S. W., Woon K. L.

Optica Applicata

2011

Vol. 41, nr 1

217--223

Significant amount of emitted light from an organic light emitting diode (OLED) is trapped as a result of total internal reflection (TIR) on a glass–air interface. One of the strategies to increase the light extraction efficiency is using a scattering thin film. A model is built using the Monte Carlo ray tracing method to simulate Mie scattering. Almost 100% of light trapped by the TIR can be extracted if the radius of the spherical scatters, the refractive index ratio between the matrix and the scatter and the concentration of the scatter are optimized. The implication is important for a high efficiency OLED used in the next generation lighting source.